The proposed research will attempt to advance our understanding of differential signalling by single neurons in metazoans, by focusing on the C. elegans neuron ASH. Models for ASH signalling with be tested by analyzing behavior worms in which ASH is the only chemosensory neuron, or in which glutamate receptor-1 (glr-1) activity is impeded. Putative genes that regulate ASH differential signalling will be sought in screens for extragenic suppressors of the glr-1(n2461) mutation. Putative genes involved in the osmosensation pathway will be sought in screens for osmosensation-defective mutants in a genetic background defective in the glr-1-encoded glutamate receptor.